1. Field of the Invention
The present invention relates generally to high-temperature vessels lined with refractory material. More specifically, the present invention relates to a method for implementation of tracking and contouring systems, automated collection of data, and processing of the measured data in either a stationary or a mobile configuration to accurately determine profiles of localized refractory thickness and/or bath height of molten material in the high-temperature vessel using the tracking system to fix the position of the contouring system with respect to the vessel.
2. State of the Art
Metallic vessels or containers of various sizes and shapes designed to hold materials having a temperature at or above the melting point of the metal are widely used in many industrial applications, as, for example, gasification processes in chemical and power production and Electric-Arc Furnaces (EAF), Basic Oxygen Furnaces (BOF), ladles, blast furnaces, degassers, and AOD furnaces in steel manufacturing. These containers are normally lined with refractory material in order to protect the metallic part of the vessel from the high-temperature content placed therein, thus extending life, making the operation safe, and increasing industrial production. During use, normal wear and tear of the refractory material requires constant inspection thereof so as to assure extended use by performing early localized repair in order to avoid catastrophic failures and unnecessary or premature refurbishment of the entire vessel's refractory lining. Before the advance of laser-based inspection techniques, inspection of ceramic linings attempting to detect unacceptable levels of lining thickness was performed visually by an experienced operator looking for dark spots in the lining indicating either high localized heat transfer rates to the refractory material or possible excessive wear and the need for lining repair, such an approach being a combination of art and science, exposing the container operator to unnecessary industrial hazards, reducing the frequency of inspections, and lacking the desired accuracy.
Costs associated with the installation and repair of ceramic linings have increased significantly over the recent past as refractory materials have been carefully engineered for each application. To improve the efficient use of refractory materials, laser-based contouring devices have been developed to measure the refractory lining thickness in these high-temperature industrial vessels or containers. Typically, such laser-based systems measure range, which is the distance from the laser source to a multitude of points inside the target vessel. If the position of the ranging system is known relative to the target vessel, the measured range information can be initially converted to contour information, i.e., the outline of the curving or irregular shape of the refractory lining exposed to the high-temperature contents of the vessel and, subsequently, to absolute refractory lining thickness if the original thickness of the refractory lining material was known or to relative variations in refractory lining thickness by comparing a subsequent measurement to one made earlier in the same container. Refractory lining thickness measurements may be subsequently used to determine where repair materials might be applied to the lining wall and to assess the relative performance of various refractory compositions developed for specific applications and localized repairs.
A typical laser-based lining thickness measuring device will employ distance measurement electronics to measure the distance or range from the measuring device to the surface of the lining of the container. In order to measure the wear in the lining, i.e., the lining's thickness, this range information taken with respect to the coordinate system or frame of reference of the measuring device has to be converted or represented in the coordinate system or frame of reference of the container or vessel. Transforming the coordinate system of the measuring device to the coordinate system of the container is sometimes referred to as “fixing.”
Depending on the application, the laser-based contouring or thickness measuring device can be mounted either permanently to a building structure near the container, e.g., a building column, or positioned on the floor next to the container whose refractory lining thickness is to be measured. Permanently mounting the measuring system is also known as a fixed-head installation. Measurements made in this configuration assume that the vessel is always going to be placed or remain in the same position or orientation relative to the instrumentation. The fixed-head approach offers the advantage of “always-on” measurement capability, simplified installation, and operation from a single, unchanging position relative to the vessel. Disadvantages of this approach include potentially limited coverage of the vessel interior and one-instrument-per-vessel installation requirements.
In U.S. Pat. No. 5,546,176 (hereinafter the '176 patent), issued on Aug. 13, 1996 and assigned to Spectra-Physics Visiontech OY, a fixing method is taught using three fixing points located at the bottom surface of the container and a laser transceiver mounted on top of a three-legged support at a fixed position away from the container. According to the method, the lining of the container is measured in such a way that, at first, a measuring device emitting and receiving optical radiation fixes the coordinate systems set for the measuring device and the container by mathematically combining the position of specific fixing points P1, P2, and P3 and angle data obtained during the measurement of the fixing points and after the rotation of the container. After the fixing, the lining on the inner surface of the container is then measured. In U.S. Pat. No. 5,570,185 (hereinafter the '185 patent), issued on Oct. 29, 1996 and also assigned to Spectra-Physics Visiontech OY, a similar method is disclosed teaching improvements for the fixing targets P1, P2, and P3 as well as placement of the laser transceiver on a carriage-like support and rails, which still maintains the distance between the transceiver and container fixed but adds the capability of moving the laser transceiver in a direction perpendicular to the line of sight of the measuring device.
Adding mobility to the measuring device is desirable because it provides multiplexing capabilities between multiple vessels and the ability to contour more of the furnace interior because the measurement position is not fixed. However, because the measurement position changes for each setup, a method is required to locate or fix the measuring device (both position and heading) relative to the vessel. Historically, this has been accomplished using fixed reference marks on the building structure surrounding the vessel or, more recently, using reference marks located on the bottom of the vessel as just explained with reference to the '185 and the '176 patents. It is known to those of ordinary skill in the art that both of these fixing approaches require operator input and, in the latter case, multiple set-ups of the target vessel, extending the total time of the contouring measurement, which in turn reduces process throughput and overall plant efficiency.